Process for preparing low-viscosity allophanates containing actinically curable groups

ABSTRACT

The present invention provides a process for preparing radiation-curing allophanates having residual monomer contents of less than 0.5% by weight and an NCO content of less than 1% by weight, wherein (A) compounds containing isocyanate groups, (B) hydroxy-functional compounds which contain groups which react, with polymerization, with ethylenically unsaturated compounds on exposure to actinic radiation (radiation-curing groups) and (C) optionally further compounds containing NCO-reactive groups, also optionally in the presence of a catalyst, are used to form NCO-group-containing urethanes having radiation-curing groups, which are subsequently reacted, without further addition of compounds containing isocyanate groups, in the presence of an allophanatization catalyst, the ratio of NCO groups of the compounds from A) to the OH groups of the compounds from B) and, where used, C) being 1.45:1.0 to 1.1:1.0.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/243,126,filed Oct. 4, 2005, which is incorporated herein by reference in itsentirety. Application Ser. No. 11/243,126 claims the benefit of GermanApplication No. 10 2004 048 873.8, filed Oct. 7, 2004, which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a simplified process for preparinglow-viscosity reaction products of polyisocyanates containing activatedgroups which react, with polymerization, with ethylenically unsaturatedcompounds on exposure to actinic radiation.

BACKGROUND OF THE INVENTION

The curing of coating systems which carry activated double bonds byactinic radiation, such as UV light, IR radiation or else electronbeams, is known and is established in industry. It is one of the mostrapid curing methods in coating technology. Coating compositions basedon this principle are thus referred to as radiation- or actinicallycuring or curable systems.

Because of the environmental and economic requirements imposed on moderncoating systems, that they should use as little organic solvents aspossible, or none at all, for adjusting the viscosity, there is a desireto use coatings raw materials which are already of low viscosity. Knownfor this purpose for a long time have been polyisocyanates with anallophanate structure as are described, inter alia, in EP-A 0 682 012.

In industry these substances are prepared by reacting a monohydric orpolyhydric alcohol with large amounts of excess aliphatic and/orcycloaliphatic diisocyanate (cf. GB-A 994 890, EP-A 0 000 194 or EP-A 0712 840). This is followed by removal of unreacted diisocyanate by meansof distillation under reduced pressure. According to DE-A 198 60 041this procedure can also be carried out with OH-functional compoundshaving activated double bonds, such as hydroxyalkyl acrylates, althoughdifficulties occur in relation to the preparation of particularlylow-monomer-content products. Since the distillation step has to takeplace at temperatures up to 135° C., in order to be able to lower theresidual isocyanate content sufficiently (<0.5% by weight of residualmonomer), it is possible for double bonds to react, with polymerization,under thermal initiation, even during the purification process, meaningthat ideal products are no longer obtained.

The preparation of low-monomer-content, allophanate-containing,polyurethane-based, radiation-curing binders is described in EP-A 0 867457 and U.S. Pat. No. 5,739,251. These binders, however, do not carryactivated double bonds but instead carry unreactive allyl ether groups(structure R—O—CH₂—CH═CH₂). It is therefore necessary to add reactivediluents (low molecular weight esters of acrylic acid), which introducethe required UV reactivity.

There has also been no paucity of attempts to prepare allophanatesindirectly, from other isocyanate derivatives, urethanes andisocyanates. For instance, EP-A 0 825 211 describes a process forsynthesizing allophanate structures from oxadiazinetriones, although nomention is made there of radiation-curing derivatives containingactivated double bonds. Transposition to the particular circumstances ofradiation-curing systems is described in German application No.:10246512.6, unpublished at the priority date of the presentspecification.

Another route is the opening of uretdiones (cf. Proceedings of theInternational Waterborne, High-Solids, and Powder Coatings Symposium2001, 28th, 405-419, and also US-A 2003 0153 713) to give allophanatestructures, which have also been already successfully transposed toradiation-curing systems (German application No.: 102004012903,unpublished at the priority date of the present specification).

Both routes require high-grade raw materials as starting material andlead only to an allophanate product which is rich in by-products.

U.S. Pat. No. 5,777,024 describes the preparation of low-viscosityradiation-curing allophanates by reacting hydroxy-functional monomerswhich carry activated double bonds with isocyanate groups ofallophanate-modified isocyanurate polyisocyanates. The radicals attachedvia the allophanate groups are saturated, and so any possible higherfunctionality is foregone.

EP-B 694 531 describes a multi-stage process for preparinghydrophilicized allophanates containing radiation-curing groups. In thatcase, however, first an NCO- and acrylate-functional urethane isprepared, which is then hydrophilicized and subsequently allophanatizedfollowing addition of a further NCO- and acrylate-functional urethane.As the process temperature for the allophanatization, temperatures of100 to 110° C. are specified.

It was the object of the present invention, then, to provide, on thebasis of readily available raw materials in one operation at a moderatetemperature of below 100° C., and without a distillation step, anNCO-group-free, high-functionality allophanate mixture containing groupscrosslinkable by actinic radiation (radiation-curing groups) as aradiation-curing binder, the intention being that this binder shouldhave a residual diisocyanate monomer content of less than 0.5% byweight. The viscosity of this product ought to be sufficiently low, i.e.below 200 000 mPas @ 23° C., that it can be processed at roomtemperature even without addition of solvent.

SUMMARY OF THE INVENTION

It has now been found that radiation-curing allophanates of this kind,meeting the above-described requirements of the objective, can beprepared specifically when certain NCO/OH ratios are maintained duringthe preparation.

The invention provides a process for preparing radiation-curingallophanates having residual monomer contents of less than 0.5% byweight and an NCO content of less than 1% by weight, wherein

A) compounds containing isocyanate groups,B) hydroxy-functional compounds which contain groups which react, withpolymerization, with ethylenically unsaturated compounds on exposure toactinic radiation (radiation-curing groups) andC) optionally further compounds containing NCO-reactive groupsD) optionally in the presence of a catalystare used to form NCO-group-containing urethanes having radiation-curinggroups, which are subsequently reacted, without further addition ofcompounds containing isocyanate groups, in the presenceE) of an allophanatization catalyst,the ratio of NCO groups of the compounds from A) to the OH groups of thecompounds from B) and, where used, C) being 1.45:1.0 to 1.1:1.0.

Further provided by the invention are the binders obtainable by theprocess of the invention.

The invention further provides coating compositions comprising

a) one or more of the radiation-curing allophanates of the invention,b) optionally one or more polyisocyanates containing free or blockedisocyanate groups, which are free from groups which react, withpolymerization, with ethylenically unsaturated compounds on exposure toactinic radiation,c) optionally other compounds, different from those of a), which containgroups which react, with polymerization, with ethylenically unsaturatedcompounds on exposure to actinic radiation, and optionally contain freeor blocked NCO groups,d) optionally one or more isocyanate-reactive compounds containingactive hydrogen,e) initiators,f) optionally solvents andg) optionally auxiliaries and additives.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As used herein, as used in the examples or unless otherwise expresslyspecified, all numbers may be read as if prefaced by the word “about”,even if the term does not expressly appear. Also, any numerical rangerecited herein is intended to include all sub-ranges subsumed therein.

The ratio of NCO groups of the compounds from A) to the OH groups of thecompounds from B) and, where used, C) is preferably 1.43:1.0 to 1.2:1.0,more preferably 1.35:1.0 to 1.3:1.0.

Suitable isocyanate-containing compounds A) include aromatic, aliphaticand cycloaliphatic polyisocyanates. Suitable polyisocyanates arecompounds of the formula Q(NCO).sub.n having a number-average molecularweight below 800 g/mol, in which n is a number from 2 to 4 and Q is anaromatic C₆-C₁₅ hydrocarbon radical, an aliphatic C₄-C₁₂ hydrocarbonradical or a cycloaliphatic C₆-C₁₅ hydrocarbon radical. Suitability ispossessed for example by diisocyanates from the series consisting of2,4-/2,6-toluene diisocyanate (TDI), methylenediphenyl diisocyanate(MDI), triisocyanatononane (TIN), naphthyl diisocyanate (NDI),4,4′-diisocyanatodicyclohexylmethane,3-isocyanatomethyl-3,3,5-trimethylcyclohexyl isocyanate(isophoronediisocyanate=IPDI), tetramethylene diisocyanate, hexamethylenediisocyanate (HDI), 2-methylpentamethylene diisocyanate,2,2,4-trimethylhexamethylene diisocyanate (THDI), dodecamethylenediisocyanate, 1,4-diisocyanatocyclohexane,4,4′-diisocyanato-3,3′-dimethyldicyclohexylmethane,2,2-bis(4-isocyanatocyclohexyl)propane,3-isocyanatomethyl-1-methyl-1-isocyanato-cyclohexane (MCI),1,3-diisooctylcyanato-4-methylcyclohexane,1,3-diisocyanato-2-methylcyclohexane and.alpha.,.alpha.,.alpha.′,.alpha.′-tetramethyl-m- or -p-xylylenediisocyanate (TMXDI) and also mixtures consisting of these compounds.

Likewise suitable as isocyanate-containing compounds A) are reactionproducts of the aforementioned isocyanates with themselves or with oneanother to form uretdiones or isocyanurates. Mention may be made by wayof example of Desmodur® N3300, Desmodur® N3400 or Desmodur® N3600 (allBayer MaterialScience, Leverkusen, DE).

Of further suitability as isocyanate-containing compounds A) arereaction products of the aforementioned isocyanates with otherisocyanate-reactive compounds to form prepolymers. Suchisocyanate-reactive compounds are, in particular, polyols, such aspolyether polyols, polyester polyols, polycarbonate polyols andpolyhydric alcohols, for example. As polyols it is possible to usehydroxyl compounds of relatively high molecular weight and, in minoramounts, hydroxyl compounds of low molecular weight as well.

The compounds of component A) can accordingly be inserted directly intothe process of the invention or, starting from an arbitrary precursor,can be prepared by preliminary reaction before the process of theinvention is carried out.

Preference is given as component A) to the use of monomericdiisocyanates. Very particular preference is given to usinghexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI) and/or4,4′-diisocyanatodicyclohexylmethane.

By actinic radiation is meant electromagnetic, ionizing radiation,especially electron beams, UV radiation and also visible light (RocheLexikon Medizin, 4th edition; Urban & Fischer Verlag, Munich 1999).

Groups which react, with polymerization, with ethylenically unsaturatedcompounds on exposure to actinic radiation (radiation-curing groups) arefor the purposes of the present invention vinyl ether, maleyl, fumaryl,maleimide, dicyclopentadienyl, acrylamide, acrylic and methacrylicgroups, preference being given to vinyl ether, acrylate and/ormethacrylate groups, more preferably acrylate groups.

Examples of suitable hydroxyl-containing compounds of component B) are2-hydroxyethyl(meth)acrylate, polyethylene oxide mono(meth)acrylate(e.g. PEA6/PEM6; Laporte Performance Chemicals Ltd., UK), polypropyleneoxide mono(meth)acrylate (e.g. PPA6, PPM5S; Laporte PerformanceChemicals Ltd., UK), polyalkylene oxide mono(meth)acrylate (e.g. PEM63P,Laporte Performance Chemicals Ltd., UK), poly(ε-caprolactone)mono(meth)acrylates such as, Tone M100® for example, (Dow, Schwalbach,DE), 2-hydroxypropyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate,hydroxybutyl vinyl ether, 3-hydroxy-2,2-dimethylpropyl (meth)acrylate,the hydroxy-functional mono-, di- or where possible higher acrylatessuch as, for example, glyceryl di(meth)acrylate, trimethylolpropanedi(meth)acrylate, pentaerythritol tri(meth)acrylate or dipentaerythritolpenta(meth)acrylate, which are obtainable by reacting polyhydric,optionally alkoxylated alcohols such as trimethylolpropane, glycerol,pentaerythritol, dipentaerythritol.

Likewise suitable as a constituent of B) as well are alcohols obtainedfrom the reaction of acids containing double bonds with epoxidecompounds optionally containing double bonds, such as, for example, thereaction products of (meth)acrylic acid with glycidyl(meth)acrylate orbisphenol A diglycidyl ether.

Additionally it is likewise possible to use unsaturated alcohols whichare obtained from the reaction of optionally unsaturated acid anhydrideswith hydroxy compounds and epoxide compounds that optionally containacrylate groups. By way of example these are the reaction products ofmaleic anhydride with 2-hydroxyethyl(meth)acrylate andglycidyl(meth)acrylate.

With particular preference the compounds of component B) correspond tothe aforementioned kind and have an OH functionality of from 0.9 to 1.1.

Preference is given to the use of hydroxyethyl (meth)acrylate,hydroxypropyl (meth)acrylate and hydroxybutyl (meth)acrylate. Veryparticular preference is given to hydroxyethyl acrylate andhydroxypropyl acrylate.

Besides the OH-functional unsaturated compounds of component B) it ispossible in the process of the invention to use further compounds C) aswell, which are different from those of B) and contain NCO-reactivegroups such as OH, SH or NH, for example.

These may be, for example, NH- or SH-functional compounds containinggroups which react, with polymerization, with ethylenically unsaturatedcompounds on exposure to actinic radiation.

Compounds which are non-reactive under exposure to actinic rays, such aspolyether polyols, polyester polyols, polycarbonate polyols andpolyhydric alcohols, for example, can also be used in addition toinfluence the product properties, as component. C). As polyols it ispossible to use hydroxyl compounds of relatively high molecular weightand, in minor amount, hydroxyl compounds of low molecular weight aswell.

Hydroxyl compounds of relatively high molecular weight include thehydroxy polyesters, hydroxy polyethers, hydroxy polythioethers, hydroxypolyacetals, hydroxy polycarbonates, dimer fatty alcohols and/oresteramides that are customary in polyurethane chemistry, in each casewith average molecular weights of 400 to 8 000 g/mol, preference beinggiven to those having average molecular weights of 500 to 6 500 g/mol.Preferred hydroxyl compounds of relatively high molecular weight arehydroxy polyethers, hydroxy polyesters and hydroxy polycarbonates.

Low molecular weight polyhydroxyl compounds which can be used arepolyols customary in polyurethane chemistry, having molecular weights of62 to 399, such as ethylene glycol, triethylene glycol, tetraethyleneglycol, propane-1,2-diol and -1,3-diol, butane-1,4-diol and -1,3-diol,hexane-1,6-diol, octane-1,8-diol, neopentyl glycol,1,4-bis(hydroxymethyl)cyclohexane,bis(hydroxymethyl)tricyclo[5.2.1.0^(2,6)]decane or1,4-bis(2-hydroxyethoxy)-benzene, 2-methyl-1,3-propanediol,2,2,4-trimethylpentanediol, 2-ethyl-1,3-hexanediol, dipropylene glycol,polypropylene glycols, dibutylene glycol, polybutylene glycols,bisphenol A, tetrabromobisphenol A, glycerol, trimethylolpropane,hexane-1,2,6-triol-butane-1,2,4-triol, pentaerythritol, quinitol,mannitol, sorbitol, methyl glycoside and 4,3,6-dianhydrohexitols.

Suitable polyether polyols are the polyethers customary in polyurethanechemistry, such as the addition compounds or mixed addition compounds,prepared using starter molecules with a valency of two to six such aswater or the abovementioned polyols or amines containing 1-to 4-NHbonds, of tetrahydrofuran, styrene oxide, ethylene oxide, propyleneoxide, the butylene oxides or epichlorohydrin, particularly those ofethylene oxide and/or of propylene oxide. Preference is given topropylene oxide polyethers which contain on average 2 to 4 hydroxylgroups and which can contain up to 50% by weight of incorporatedpolyethylene oxide units.

Examples of suitable polyester polyols include reaction products ofpolyhydric, preferably dihydric and optionally additionally trihydricalcohols with polybasic, preferably dibasic, carboxylic acids. In lieuof the free carboxylic acids it is also possible to use thecorresponding polycarboxylic anhydrides or corresponding polycarboxylicesters of lower alcohols or mixtures thereof for preparing thepolyesters. The polycarboxylic acids may be aliphatic, cycloaliphaticaromatic and/or heterocyclic in nature and may where appropriate besubstituted, by halogen atoms for example, and/or unsaturated. By way ofexample mention is made of adipic acid, phthalic acid, isophthalic acid,succinic acid, suberic acid, azelaic acid, sebacic acid, trimelliticacid, phthalic anhydride, tetrahydrophthalic anhydride, glutaricanhydride, tetrachlorophthalic anhydride,endomethylenetetrahydrophthalic anhydride, maleic anhydride, maleicacid, fumaric acid, dimeric and trimeric fatty acids such as oleic acid,optionally in a mixture with monomeric fatty acids, dimethylterephthalate or bis-glycol terephthalate. Preference is given tohydroxy polyesters which melt at below 60° C. and have 2 or 3 terminalOH groups.

The polycarbonate polyols that come under consideration are obtainableby reacting carbonic acid derivatives, e.g. diphenyl carbonate, dimethylcarbonate or phosgene, with diols. Examples of suitable such diolsinclude ethylene glycol, triethylene glycol, tetraethylene glycol,propane-1,2-diol and -1,3-diol, butane-1,4-diol and -1,3-diol,pentane-1,5-diol, hexane-1,6-diol, octane-1,8-diol, neopentyl glycol,1,4-bis(hydroxymethyl)cyclohexane,bis(hydroxymethyl)tricyclo[5.2.1.0^(2,6)]decane or1,4-bis(2-hydroxyethoxy)-benzene, 2-methyl-1,3-propanediol,2,2,4-trimethylpentanediol, dipropylene glycol, polypropylene glycols,dibutylene glycol, polybutylene glycols, bisphenol A andtetrabromobisphenol A, or mixtures of said diols. The diol componentpreferably receives 40% to 100% by weight of hexanediol, preferablyhexane-1,6-diol, and/or hexanediol derivatives, preferably those whichin addition to terminal OH groups contain ether groups or ester groups,examples being products obtained by reacting 1 mol of hexanediol with atleast 1 mol, preferably 1 to 2 mol, of caprolactone in accordance withDE-A 1 770 245, or by etherifying hex anediol with itself to give thedi- or trihexylene glycol. The preparation of such derivatives is knownfor example from DE-A 1 570 540. The polyether-polycarbonate diolsdescribed in DE-A 3 717 060 can also be used to very good effect.

The hydroxypolycarbonates ought to be substantially linear. As a resultof the incorporation of polyfunctional components, in particular polyolsof low molecular weight, however, they may also, optionally, be slightlybranched.

Examples of compounds suitable for this purpose includetrimethylolpropane, hexane-1,2,6-triol, glycerol, butane-1,2,4-triol,pentaerythritol, quinitol, mannitol, sorbitol, methyl glycoside and4,3,6-dianhydrohexitols.

Additionally it is possible to incorporate groups having ahydrophilicizing action, particularly if use from an aqueous medium isenvisaged, such as in an aqueous coating material, for example. Groupswith a hydrophilicizing action are ionic groups, which may be eithercationic or anionic in nature, and/or nonionic hydrophilic groups.Cationically, anionically or nonionically dispersing compounds are thosewhich contain, for example, sulphonium, ammonium, phosphonium,carboxylate, sulphonate or phosphonate groups or the groups which can beconverted into the aforementioned groups by forming salts (potentiallyionic groups) or which contain polyether groups and can be incorporatedby means of existing isocyanate-reactive groups. Isocyanate-reactivegroups of preferred suitability are hydroxyl and amino groups.

Examples of suitable compounds containing ionic or potentially ionicgroups are mono- and dihydroxycarboxylic acids, mono- anddiaminocarboxylic acids, mono- and dihydroxysuilphonic acids, mono- anddiaminosulphonic acids and also mono- and dihydroxyphosphonic acids ormono- and diaminophosphonic acids and their salts, such as dimethylolpropionic acid, dimethylolbutyric acid, hydroxypivalic acid,N-(2-aminoethyl)-β-alanine, 2-(2-aminoethylamino)ethanesulphonic acid,ethylenediamine-propyl- or butylsulphonic acid, 1,2- or1,3-propylenediamine-β-ethylsulphonic acid, malic acid, citric acid,glycolic acid, lactic acid, glycine, alanine, taurine, lysine,3,5-diaminobenzoic acid, an adduct of IPDI and acrylic acid (EP-A 0 916647, Example 1) and its alkali metal and/or ammonium salts; the adductof sodium bisulphite with but-2-ene-1,4-diol, polyethersulphonate, thepropoxylated adduct of 2-butenediol and NaHSO₃, described for example inDE-A 2 446 440 (page 5-9, formula I-III) and also structural units whichcan be converted into cationic groups, such as N-methyldiethanolamine,as hydrophilic synthesis components. Preferred ionic or potential ioniccompounds are those possessing carboxyl or carboxylate and/or sulphonategroups and/or ammonium groups.

Particularly preferred ionic compounds are those which contain carboxyland/or sulphonate groups as ionic or potentially ionic groups, such asthe salts of N-(2-aminoethyl)-β-alanine, of2-(2-aminoethylamino)ethanesulphonic acid or of the adduct of IPDI andacrylic acid (EP-A-0 916 647, Example 1) and also of dimethylolpropionicacid.

Suitable nonionically hydrophilicizing compounds are, for example,polyoxyalkylene ethers containing at least one hydroxyl or amino group.These polyethers include a fraction of from 30% to 100% by weight ofunits derived from ethylene oxide. Suitable compounds include polyethersof linear construction with a functionality of between 1 and 3, but alsocompounds of the general formula (I),

in whichR¹ and R² independently of one another are each a divalent aliphatic,cycloaliphatic or aromatic radical having 1 to 18 carbon atoms, whichmay be interrupted by oxygen and/or nitrogen atoms, andR³ is an alkoxy-terminated polyethylene oxide radical.

Nonionically hydrophilicizing compounds are, for example, alsomonohydric polyalkylene oxide polyether alcohols containing on average 5to 70, preferably 7 to 55, ethylene oxide units per molecule, such asare obtainable in conventional manner by alkoxylating suitable startermolecules (e.g. in Ullmanns Encyclopadie der technischen Chemie, 4thedition, volume 19, Verlag Chemie, Weinheim pp. 31-38).

Examples of suitable starter molecules are saturated monoalcohols suchas methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol,sec-butanol, the isomers pentanols, hexanols, octanols and nonanols,n-decanol, n-dodecanol, n-tetradecanol, n-hexadecanol, n-octadecanol,cyclohexanol, the isomeric methylcyclohexanols orhydroxylmethylcyclohexane, 3-ethyl-3-hydroxymethyloxetane ortetrahydrofurfuryl alcohol, diethylene glycol monoalkyl ethers such as,for example, diethylene glycol monobutyl ether, unsaturated alcoholssuch as allyl alcohol, 1,1-dimethylallyl alcohol or oleyl alcohol,aromatic alcohols such as phenol, the isomeric cresols ormethoxyphenols, araliphatic alcohols such as benzyl alcohol, anisylalcohol or cinnamyl alcohol, secondary monoamines such as dimethylamine,diethylamine, dipropylamine, diisopropylamine, dibutylamine,bis(2-ethylhexyl)amine, N-methyl- and N-ethylcyclohexylamine ordicyclohexylamine and also heterocyclic secondary amines such asmorpholine, pyrrolidine, piperidine or 1H-pyrazole. Preferred startermolecules are saturated monoalcohols. Particular preference is given tousing diethylene glycol monobutyl ether as starter molecule.

Alkylene oxides suitable for the alkoxylation reaction are, inparticular, ethylene oxide and propylene oxide, which can be used in anyorder or in a mixture in the alkoxylation reaction.

The polyalkylene oxide polyether alcohols are either straightpolyethylene oxide polyethers or mixed polyalkylene oxide polyethers atleast 30 mol %, preferably at least 40 mol %, of whose alkylene oxideunits are composed of ethylene oxide units. Preferred nonionic compoundsare monofunctional mixed polyalkylene oxide polyethers which contain atleast 40 mol % of ethylene oxide units and not more than 60 mol % ofpropylene oxide units.

Especially when using a hydrophilicizing agent containing ionic groupsit is necessary to investigate its effect on the action of the catalystsD) and E). For this reason preference is given to nonionic compounds ashydrophilicizing agents.

Suitable compounds of the catalyst component D) include urethanizationcatalysts that are known per se to the skilled person, such as organotincompounds or aminic catalysts. Organotin compounds that may be mentionedby way of example include the following: dibutyltin diacetate,dibutyltin dilaurate, dibutyltin bis-acetoacetonate and tin carboxylatessuch as tin octoate, for example. The tin catalysts mentioned mayoptionally be used in combination with aminic catalysts such asaminosilanes or 1,4-diazabicyclo[2.2.2]octane.

With particular preference dibutyltin dilaurate is used asurethanization catalyst in D).

In the process of the invention the catalyst D), if used at all, isemployed in amounts of 0.001% to 5.0%, preferably 0.001% to 0.1% andmore preferably 0.005%-to 0.05% by weight, based on solids content ofthe process product.

As catalyst E) it is possible to use allophanatization catalysts thatare known per se to the skilled person, such as the zinc salts zincoctoate, zinc acetylacetonate and zinc 2-ethylcaproate, ortetraalkylammonium compounds, such asN,N,N-trimethyl-N-2-hydroxypropylammonium hydroxide,N,N,N-trimethyl-N-2-hydroxypropylammonium 2-ethylhexanoate or choline2-eihylhexanoate. Preference is given to the use of thetetraalkylammonium compounds, more preferably that of tetraalkylammoniumalkarioates and very preferably that of choline 2-ethylhexanoate asallophanatization catalyst.

The allophanatization catalyst is used in amounts of 0.001-5.0% byweight, preferably 0.01-1.0% by weight and more preferably 0.05-0.5% byweight based on solids content of the process product.

In principle it is possible to use the allophanatization catalyst E)even for the urethanization reaction in D) and to simplify the two-stageprocedure into a one-stage reaction. However, this is not preferred, andso the allophanatization catalyst is not added until all or a proportionof the urethane groups are to be reacted to allophanate groups.

The catalyst E) can be added in a portion all at once or else in-anumber of portions or else continuously. Preference is given toportionwise or continuous addition, in order to avoid temperature peaksand consequent unwanted polymerization reactions of the radiation-curinggroups. With particular preference the catalyst E) is added at a rate of200-600 ppm/h and in order to complete the allophanatization thereaction mixture is stirred on until the desired NCO content of the endproduct is reached.

The reaction of allophanatization is preferably carried out until theNCO content of the product is below 0.5% by weight, more preferablybelow 0.1% by weight.

It is possible in principle to react a residual NCO group content withNCO-reactive compounds such as alcohols, for example, after the end ofthe allophanatization reaction. This gives products having a speciallylow NCO contents.

It is also possible to apply the catalysts D) and/or E) to supportmaterials by methods known to the skilled person and to use them asheterogeneous catalysts.

It is possible to make use optionally at any desired point of solventsor reactive diluents.

Suitable solvents are inert towards the functional groups present in theprocess product from the time of their addition up to the end of theprocess. Suitable solvents are, for example, those used in the paintindustry, such as hydrocarbons, ketones and esters, e.g. toluene,xylene, isooctane, acetone, butanone, methyl isobutyl ketone, ethylacetate, butyl acetate, tetrahydrofuran, N-methylpyrrolidone,dimethylacetamide and dimethylformamide, though it is preferred not toadd any solvent.

As reactive diluents it is possible to use compounds which in the courseof UV curing are likewise (co)polymerized and hence incorporated intothe polymer network and are inert towards NCO groups. Such reactivediluents are described exemplarily, by way of example, in P. K. T.Oldring (Ed.), Chemistry & Technology of UV & EB Formulations ForCoatings, Inks & Paints, Vol. 2, 1991, SITA Technology, London, pp.237-285. They may be esters of acrylic acid or methacrylic acid,preferably of acrylic acid, with mono- or polyfunctional alcohols.Examples of suitable alcohols include the isomeric butanols, pentanols,hexanols, heptanols, octanols, nonanols and decanols, and alsocycloaliphatic alcohols such as isobornol, cyclohexanol and alkylatedcyclohexanols, dicyclo-pentanol, arylaliphatic alcohols such asphenoxyethanol and nonylphenylethanol, and tetrahydrofurfuryl alcohols.Additionally it is possible to use alkoxylated derivatives of thesealcohols. Suitable dihydric alcohols are, for example, alcohols such asethylene glycol, propane-1,2-diol, propane-1,3-diol, diethylene glycol,dipropylene glycol, the isomeric butanediols, neopentyl glycol,hexane-1,6-diol, 2-ethylhexanediol and tripropylene glycol or elsealkoxylated derivatives of these alcohols. Preferred dihydric alcoholsare hexane-1,6-diol, dipropylene glycol and tripropylene glycol.Suitable trihydric alcohols are glycerol or trimethylolpropane or theiralkoxylated derivatives. Tetrahydric alcohols are pentaerythritol or itsalkoxylated derivatives.

The binders of the invention must be stabilized against prematurepolymerization. Therefore, as a constituent of component A) or B),before and/or during the reaction, stabilizers are added which inhibitthe polymerization. Use is made in this context preferably ofphenothiazine. Possible other stabilizers are phenols such aspara-methoxyphenyl, 2,5-di-tert-butylhydroquinone or2,6-di-tert-butyl-4-methylphenol. Also suitable are N-oxyl compounds forstabilization, such as 2,2,6,6-tetramethylpiperidine N-oxide (TEMPO),for example, or its derivatives. The stabilizers can also beincorporated chemically into the binder; suitability in this context ispossessed by compounds of the abovementioned classes, especially if theystill carry further free aliphatic alcohol groups or primary orsecondary amine groups and hence can be attached chemically to compoundsof component A) by way of urethane or urea groups. Particularly suitablefor-this purpose is 2,2,6,6-tetramethyl-4-hydroxypiperidine N-oxide.

Other stabilizers, such as compounds from the class of the HALS(HALS=hindered amine light stabilizers), in contrast, are used lesspreferably in E), since they are known not to enable such effectivestabilization and instead may lead to “creeping” free-radicalpolymerization of unsaturated groups.

The stabilizers are to be chosen such that they are stable under theinfluence of the catalysts D) and E) and do not react with a componentof the process of the invention under the reaction conditions. This canlead to a loss of the stabilizing property.

In order to stabilize the reaction mixture, in particular theunsaturated groups, against premature polymerization it is possible topass an oxygen-containing gas, preferably air, into and/or over thereaction mixture. It is preferred for the gas to have a very lowmoisture content, in order to prevent unwanted reaction in the presenceof isocyanate.

In general a stabilizer is added during the preparation of the bindersof the invention, and at the end, in order to achieve a long-termstability, stabilization is repeated with a phenolic stabilizer, andoptionally the reaction product is saturated with air.

In the process of the invention the stabilizer component is usedtypically in amounts of 0.001% to 5.0% by weight, preferably 0.01% to2.0% by weight and more preferably 0.05% to 1.0% by weight, based on thesolids content of the process product.

The process of the invention is carried out at temperatures of not morethan 100° C., preferably of 20 to 100° C., more preferably of 40 to 100°C., in particular at 60 to 90° C.

It is immaterial whether one or both stages of the process of theinvention is or are carried out continuously in for example a staticmixer, extruder or compounder or batchwise in for example a stirredreactor.

Preferably the process of the invention is carried out in a stirredreactor.

The course of the reaction can be monitored by means of suitablemeasuring instruments installed in the reaction vessel and/or on thebasis of analyses on samples taken. Suitable techniques are known to theskilled person. They include, for example, viscosity measurements,measurements of the NCO content, of the refractive index, of the OHcontent, gas chromatography (GC), nuclear magnetic resonancespectroscopy (NMR), infrared spectroscopy (IR) and near infraredspectroscopy (NIR). Preference is given to IR checking for free NCOgroups present (for aliphatic NCO groups, band at approximately v=2272cm⁻¹) and to GC analyses for unreacted compounds from A), B) and, whereused, C).

It is possible in principle to carry out the process of the invention inone stage, operating with a catalyst or a catalyst mixture thatcatalyses both the urethanization reaction and the allophanatizationreaction. In that case urethanization and allophanatization are carriedout in parallel. This procedure, though, is not preferred.

The unsaturated allophanates obtainable by the process of the invention,especially those based on the HDI employed with preference, preferablyhave shear viscosities at 23° C. of ≦150 000 mPas, more preferably ≦80000 mPas.

The unsaturated allophanates obtainable by the process of the invention,especially those based on the HDI used with preference, preferably havenumber-average molecular weights M.sub.n of 600 to 3000 g/mol, morepreferably 650 to 1500 g/mol.

The unsaturated allophanates obtainable by the process of the inventionpreferably contain less than 0.5% by weight of free di- and/ortriisocyanate monomers, more preferably less than 0.1% by weight.

The radiation-curing allophanates of the invention can be used forproducing coatings and paints and also adhesives, printing inks, castingresins, dental compounds, sizes, photoresists, stereolithographysystems, resins for composite materials and sealants. In the case ofadhesive bonding or sealing, however, a requirement is that, in the caseof UV radiation curing, at least one of the two substrates to be bondedor sealed to one another is permeable to UV radiation; in other words,in general, it must be transparent. In the case of electron beams,sufficient permeability for electrons should be ensured. Preference isgiven to use in paints and coatings.

The invention further provides coating compositions comprising

a) one or more of the radiation-curing allophanates of the invention,b) optionally one or more polyisocyanates containing free or blockedisocyanate groups, which are free from groups which react, withpolymerization, with ethylenically unsaturated compounds on exposure toactinic radiation,c) optionally other compounds, different from those of a), which containgroups which react, with polymerization, with ethylenically unsaturatedcompounds on exposure to actinic radiation, and optionally contain freeor blocked NCO groups,d) optionally one or more isocyanate-reactive compounds containingactive hydrogen,e) initiators,f) optionally solvents andg) optionally auxiliaries and additives.

The polyisocyanates of component b) are known per se to the skilledperson. Preference is given here to using compounds optionally modifiedwith isocyanurate, allophanate, biuret, uretdione and/oriminooxadiazinetrione groups and based on hexamethylene diisocyanate,isophorone diisocyanate, 4,4′-diisocyanatodicyclohexylmethane and/ortrimethylhexamethylene diisocyanate.

The NCO groups in this case may also be blocked, blocking agentsemployed being the compounds already mentioned in connection with thedescription of component A).

The compounds of component c) include compounds such as, in particular,urethane acrylates based preferably on hexamethylene diisocyanate,isophorone diisocyanate, 4,4′-diisocyanatodicyclohexylmethane and/ortrimethylhexamethylene diisocyariate, which optionally may have beenmodified with isocyanurate, allophanate, biuret, uretdione and/oriminooxadiazinetrione groups, and which contain noisocyanate-group-reactive functions containing active hydrogen.

NCO-containing urethane acrylates are available commercially from BayerAG, Leverkusen, DE as Roskydal® UA VP LS 2337, Roskydal® UA VP LS 2396or Roskydal® UA XP 2510.

Additionally the reactive diluents already described and known in theart of radiation-curing coatings may be used as a constituent of c),provided that they do not contain any NCO-reactive groups.

Compounds of component d) can be saturated or unsaturated. Chemicalfunctionalities reacting with NCO groups are functionalities containingactivated hydrogen atoms, such as hydroxyl, amine or thiol.

Preference is given to saturated polyhydroxy compounds, examples beingthe polyetherpolyols, polyesterpolyols, polycarbonatepolyols,poly(meth)acrylatepolyols and/or polyurethanepolyols which are knownfrom the technology of coating, adhesive bonding, printing inks orsealants and which contain no groups which react, with polymerization,with ethylenically unsaturated compounds on exposure to actinicradiation.

Unsaturated hydroxy-functional compounds are, for example, the epoxyacrylates, polyester acrylates, polyether acrylates, urethane acrylatesand acrylated polyacrylates which are known in the art ofradiation-curing coatings and have an OH number of from 30 to 300 mgKOH/g.

It is additionally possible to use the reactive diluents, alreadydescribed and known in the art of radiation-curing coatings, as aconstituent of d), provided that they contain NCO-reactive groups.

As initiators of component e) for a free-radical polymerization it ispossible to employ initiators which can be activated thermally and/or byradiation. Photoinitiators, which are activated by UV or visible light,are preferred in this context. Photoinitiators are compounds known perse, being sold commercially, a distinction being made betweenunimolecular (type I) and bimolecular (type II) initiators. Suitable(type I) systems are aromatic ketone compounds, e.g. benzophenones incombination with tertiary amines, alkylbenzophenones,4,4′-bis(dimethylamino)benzophenone (Michler's ketone), anthrone andhalogenated benzophenones or mixtures of the types stated. Of furthersuitability are (type II) initiators such as benzoin and itsderivatives, benzil ketals, acylphosphine oxides,2,4,6-trimethylbenzoyldiphenylphosphine oxide for example,bisacylphosphine oxides, phenylglyoxylic esters, camphorquinone,.α-aminoalkylphenones, α,α-dialkoxyacetophenones andα-hydroxyalkylphenones.

The initiators, which are used in amounts between 0.1% and 10% byweight, preferably 0.1% to 5% by weight, based on the weight of thefilm-forming binder, can be used as an individual substance or, onaccount of frequent advantageous synergistic effects, in combinationwith one another.

Where electron beams-are used instead of UV radiation there is no needfor a photoinitiator. Electron beams, as is known to the skilled person,are generated by means of thermal emission and accelerated by way of apotential difference. The high-energy electrons then pass through atitanium foil and are guided onto the binders to be cured. The generalprinciples of electron beam curing are described in detail in “Chemistry& Technology of UV & EB Formulations for Coatings, Inks & Paints”, Vol.1, P K T Oldring (Ed.), SITA Technology, London, England, pp. 101-157,1991.

In the event of thermal curing of the activated double bonds, this canalso take place with addition of thermally decomposing free-radicalinitiators. Suitability is possessed, as is known to the skilled person,by, for example, peroxy compounds such as dialkoxy dicarbonates such as,for example, bis(4-tert-butylcyclohexyl)peroxydicarbonate, dialkylperoxides such as, for example, dilauryl peroxide, peresters of aromaticor aliphatic acids such as, for example, tert-butyl perbenzoate ortert-amyl peroxy 2-ethylhexanoate, inorganic peroxides such as, forexample, ammonium peroxodisulphate, potassium peroxodisulphate, organicperoxides such as, for example, 2,2-bis(tert-butylperoxy)butane, dicumylperoxide, tert-butyl hydroperoxide or else azo compounds such as2,2′-azobis[N-(2-propenyl)-2-methylpropionamides],1-[(cyano-1-methylethyl)azo]formamides,2,2′-azobis(N-butyl-2-methylpropionamides),2,2′-azobis(N-cyclohexyl-2-methyl-propionamides), 2,2′-azobis{2-methyl-N-[2-(1-hydroxybutyl)]propionamides}, 2,2′-azobis{2-methyl-N-[2-(1-hydroxybutyl)]propionamides, 2,2′-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamides. Alsopossible are highly substituted 1,2-diphenylethanes(benzpinacols), suchas, for example, 3,4-dimethyl-3,4-diphenylhexane,1,1,2,2-tetraphenylethane-1,2-diol or else the silylated derivativesthereof.

It is also possible to use a combination of initiators activable by UVlight and thermally.

The auxiliaries and additives of component e) include solvents of thetype specified above.

Additionally it is possible for e), in order to increase the weatherstability of the cured coating film, to comprise UV absorbers and/orHALS stabilizers as well. Preference is given to the combination. Theformer ought to have an absorption range of not more than 390 nm, suchas triphenyltriazine types (e.g. Tinuvin® 400 (Ciba SpezialitatenchemieGmbH, Lampertheim, DE)), benzotriazoles such as Tinuvin® 622 (CibaSpezialitatenchemie GmbH, Lampertheim, DE) or oxalic dianilides (e.g.Sanduvor® 3206 (Clariant, Muttenz, CH))) and are added at 0.5%-3.5% byweight, based on resin solids. Suitable HALS stabilizers are availablecommercially (Tinuvin® 292 or Tinuvin® 123 (Ciba SpezialitatenchemieGmbH, Lampertheim, DE) or Sanduvor® 3258 (Clariant, Muttenz, CH).Preferred amounts are 0.5%-2.5% by weight based on resin solids.

It is likewise possible for e) to comprise pigments, dyes, fillers,levelling additives and devolatilizing additives.

Additionally it is possible, if necessary, for the catalysts known frompolyurethane chemistry for accelerating the NCO/OH reaction to bepresent in e). These are, for example, tin salts or zinc salts ororganotin compounds, tin soaps and/or zinc soaps such as, for example,tin octoate, dibutyltin dilaurate, dibutyltin oxide or tertiary aminessuch as diazabicyclo[2.2.2]octane (DABCO).

The application of the coating compositions of the invention to thematerial to be coated takes place with the methods known and customaryin coatings technology, such as spraying, knife coating, rolling,pouring, dipping, spin coating, brushing or squirting or by means ofprinting techniques such as screen, gravure, flexographic or offsetprinting and also by means of transfer methods.

Suitable substrates are, for example, wood, metal, including inparticular metal as used in the applications of wire enamelling, coilcoating, can coating or container coating, and also plastic, includingplastic in the form of films, especially ABS, AMMA, ASA, CA, CAB, EP,UF, CF, MF, MPF, PF, PAN, PA, PE, HDPE, LDPE, LLDPE, UHMWPE, PET, PMMA,PP, PS, SB, PUR, PVC, RF, SAN, PBT, PPE, POM, PUR-RIM, SMC, BMC,PP-EPDM, and UP (abbreviations according to DIN 7728T1), paper, leather,textiles, felt, glass, wood, wood materials, cork, inorganically bondedsubstrates such as wooden boards and fibre cement slabs, electronicassemblies or mineral substrates. It is also possible to coat substratesconsisting of a variety of the abovementioned materials, or to coatalready coated substrates such as vehicles, aircraft or boats and alsoparts thereof, especially vehicle bodies or parts for exterior mounting.It is also possible to apply the coating compositions to a substratetemporarily, then to cure them partly or fully and optionally to detachthem again, in order to produce films, for example.

For curing it is possible for solvents present, for example, to beremoved entirely or partly by flashing off.

Subsequently or simultaneously it is possible for the optionallynecessary thermal and photochemical curing operation or operations to becarried out in succession or simultaneously.

If necessary the thermal curing can take place at room temperature orelse at elevated temperature, preferably at 40 to 160° C., morepreferably at 60 to 130° C., very preferably at 80 to 110° C.

Where photoinitiators are used in d) the radiation cure takes placepreferably by exposure to high-energy radiation, in other words UVradiation or daylight, such as light of wavelength 200 to 700 nm or bybombardment with high-energy electrons (electron beams, 150 to 300 keV).Radiation sources of light or UV light used are, for example,high-pressure or medium-pressure mercury vapour lamps, it being possiblefor the mercury vapour to have been modified by doping with otherelements such as gallium or iron. Lasers, pulsed lamps (known under thedesignation of UV flashlight lamps), halogen lamps or excimer emittersare likewise possible. As an inherent part of their design or throughthe use of special filters and/or reflectors, the emitters may beequipped so that part of the UV spectrum is prevented from beingemitted. By way of example, for reasons of occupational hygiene, forexample, the radiation assigned to UV-C or to UV-C and UV-B may befiltered out. The emitters may be installed in stationary fashion, sothat the material for irradiation is conveyed past the radiation sourceby means of a mechanical device, or the emitters may be mobile and thematerial for irradiation may remain stationary in the course of curing.The radiation dose which is normally sufficient for crosslinking in thecase of UV curing is situated in the range from 80 to 5000 mJ/cm².

Irradiation can if desired also be carried out in the absence of oxygen,such as under an inert gas atmosphere or an oxygen-reduced atmosphere.Suitable inert gases are preferably nitrogen, carbon dioxide, noblegases or combustion gases. Irradiation may additionally take place bycovering the coating with media transparent to the radiation. Examplesof such are, for example, polymeric films, glass or liquids such aswater.

Depending on the radiation dose and curing conditions it is possible tovary the type and concentration of any initiator used, in a manner knownto the skilled person.

Particular preference is given to carrying out curing usinghigh-pressure mercury lamps in stationary installations. Photoinitiatorsare then employed at concentrations of from 0.1% to 10% by weight, morepreferably from 0.2% to 3.0% by weight, based on the solids of thecoating. For curing these coatings it is preferred to use a dose of from200 to 3000 mJ/cm², measured in the wavelength range from 200 to 600 nm.

In the case of use of thermally activable initiators in d) the curingcan be carried out by increasing the temperature. The thermal energy mayin this case be introduced into the coating by means of radiation,thermal conduction and/or convection, it being customary to employ theinfrared lamps, near-infrared lamps and/or ovens that are conventionalin coatings technology.

The applied film thicknesses (prior to curing) are typically between 0.5and 5000 .mu.m, preferably between 5 and 1000 μm, more preferablybetween 15 and 200 μm. Where solvents are used, it is removed afterapplication and before curing, by the customary methods.

EXAMPLES

All percentages are by weight unless indicated otherwise.

The determination of the NCO contents in % was undertaken byback-titration with 0.1 mol/1 hydrochloric acid following reaction withbutylamine, on the basis of DIN EN ISO 11909.

The viscosity measurements were carried out with a plate-plateviscometer Roto Visko 1 from Haake, DE in accordance with ISO/DIS3219:1990.

The ambient temperature of 23° C. prevailing at the time when theexperiments were conducted is referred to as RT.

Preparation of Choline 2-Ethylhexanoate

In a 1000 ml glass flask with stirring apparatus 83 g of sodium2-ethylhexanoate were dissolved at RT in 600 ml of methanol.Subsequently 69.8 g of choline chloride were added in portions and themixture was stirred at room temperature for a further 10 hours. Theprecipitate formed was filtered off and the solution was concentrated toroughly a third under reduced pressure on a rotary evaporator untilagain a precipitate formed. Dilution took place with about 400 ml ofacetone, followed by filtration again, and the solvent was againstripped off under reduced pressure. The residue which remained wasagain taken up in about 400 ml of acetone, followed by filtration, andthe solvent was stripped off. This gave 117 g of crystallization-stable,liquid product which was used in this form as an allophanatizationcatalyst.

Example 1 Inventive Allophanate-Containing Binder (NCO/OH=1.33:1)

A 500-ml four-necked glass flask with reflux condenser, heatable oilbath, mechanical stirrer, air traversal (l/h), internal thermometer anddropping funnel was charged with 231.16 g of hexamethylene diisocyanate(Desmodur® H, Bayer MaterialScience, Leverkusen) and 50 mg ofphenothiazine and this initial charge was heated to 70° C. 25 mg ofdibutyltin dilaurate (Desmorapid Z, Bayer MaterialScience, Leverkusen)were added and 268.01 g of hydroxypropyl acrylate were added dropwise ata rate such that the temperature did not exceed 80° C.

Stirring was then continued until the theoretical NCO value of 5.77% wasreached. Subsequently the temperature was raised to 80° C. and over 6hours 0.75 g of choline 2-ethylhexanoate was slowly metered in. Afterabout more than half the time a distinct exotherm was observed, whichnecessitated cooling of the mixture. Despite this, metering wascompleted, and was followed by stirring for an additional two hours.This gave a colourless resin having a residual NCO content of 0.1% and aviscosity of 75,400 mPas (23° C.).

Example 2 Inventive Allophanate-Containing Binder (NCO/OH=1.25:1)

A 500-ml four-necked glass flask with reflux condenser, heatable oilbath, mechanical stirrer, air traversal (l/h), internal thermometer anddropping funnel was charged with 223.18 g of hexamethylene diisocyanateand 50 mg of phenothiazine and this initial charge was heated to 70° C.25 mg of dibutyltin dilaurate were added and 276.00 g of hydroxypropylacrylate were added dropwise at a rate such that the temperature did notexceed 80° C. Stirring was then continued until the theoretical NCOvalue of 4.46% was reached. Subsequently at 70° C. over 6 hours 0.75 gof choline 2-ethylhexanoate was slowly metered in. Towards the end ofthe time a distinct exotherm was observed, which necessitated cooling ofthe mixture. Despite this, metering was completed, and was followed bystirring for an additional two hours. This gave a colourless resinhaving a residual NCO content of 0.05% and a viscosity of 35,800 mPas(23° C.).

Example 3 Inventive Allophanate-Containing Binder (NCO/OH=1.43:1)

A 500-ml four-necked glass flask with reflux condenser, heatable oilbath, mechanical stirrer, air traversal (l/h), internal thermometer anddropping funnel was charged with 239.74 g of hexamethylene diisocyanateand 50 mg of phenothiazine and this initial charge was heated to 70° C.25 mg of dibutyltin dilaurate were added and 259.43 g of hydroxypropylacrylate were added dropwise at a rate such that the temperature did notexceed 80° C. Stirring was then continued until the theoretical NCOvalue of 7.18% was reached. Subsequently at 70° C. over 6 hours 0.75 gof choline 2-ethylhexanoate was slowly metered in. After about more thanhalf the time a distinct exotherm was observed, which necessitatedcooling of the mixture. Despite this, metering was completed, and wasfollowed by stirring for an additional hour. This gave a colourlessresin having a residual NCO content of 0.0% and a viscosity of 125,000mPas (23° C.).

Comparative Example to Example 1-3 Non-Inventive Allophanate-ContainingBinder (NCO/OH=1.6:1)

A 500-ml four-necked glass flask with reflux condenser, heatable-oilbath, mechanical stirrer, air traversal (l/h), internal thermometer anddropping funnel was charged with 268.8 g of hexamethylene diisocyanateand 50 mg of phenothiazine and this initial charge was heated to 70° C.25 mg of dibutyltin dilaurate were added and 260.0 g of hydroxypropylacrylate were added dropwise at a rate such that the temperature did notexceed 80° C. Stirring was then continued until the theoretical NCOvalue of 9.53% was reached. Subsequently at 70° C. over 6 hours 0.75 gof choline 2-ethylhexanoate was slowly metered in. Towards the end ofthe time a distinct exotherm was observed, which necessitated cooling ofthe mixture. Despite this, metering was completed, and was followed bystirring for an additional two hours. This gave a colourless resinhaving a residual NCO content of 0.05% and a viscosity, extremelydifficult to measure, of about 650,000 mPas (23° C.).

Example 4 Inventive Allophanate-Containing Binder (Hybrid Type,NCO/OH=1.33:1)

A 500-ml four-necked glass flask with reflux condenser, heatable oilbath, mechanical stirrer, air traversal (l/h), internal thermometer anddropping funnel was charged with a mixture of 107.59 g of hexamethylenediisocyanate and 142.02 of isophorone diisocyanate (Desmodur® I, BayerMaterialScience, Leverkusen) with 250 mg of phenothiazine and thisinitial charge was heated to 70° C. 50 mg of dibutyltin dilaurate wereadded and 249.49 g of hydroxypropyl acrylate were added dropwise at arate such that the temperature did not exceed 80° C. Stirring wascontinued until the theoretical NCO value of 5.37% was reached.Subsequently the temperature was raised to 80° C. and over 4 hours 0.75g of choline 2-ethylhexanoate was slowly metered in. After about halfthe time a distinct exotherm was observed, which necessitated cooling ofthe mixture. After the end of the metering, stirring was continued foran additional two hours and dilution took place with 125 g of hexanedioldiacrylate (Laromer® HDDA, BASF AG, Ludwigshafen, Del.). This gave ayellowish resin having a residual NCO content of 0.17% and a viscosityof 20,500 mPas (23° C.).

Example 5 Coating Formulation and Coating Material

A portion of the product from Example 1 was mixed thoroughly with 3.0%of the photoinitiator Darocur® 1173 (photoinitiator, commercial productof Ciba Spezialitatenchemie GmbH, Lampertheim, DE). Using a bone doctorblade with a gap of 90 .mu.m the mixture was drawn down in the form of athin film onto a glass plate. UV irradiation (medium pressure mercurylamp, IST Metz GmbH, Nurtingen, Del., 750 mJ/cm.sup.2) gave a hard,transparent coating which could hardly be damaged by scratching usingsteel wool (grade 0/0/0) in ten back-and-forth strokes with a force of500 g directed onto the film.

Although the invention has been described in detail in the foregoing forthe purpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention except as it may be limited by the claims.

1. A radiation-curing allophanate having a residual monomer content ofless than 0.5% by weight and an NCO content of less than 1% by weight,obtained by a process comprising forming an NCO-group-containingurethane having radiation forming groups, by reacting, optionally in thepresence of a catalyst, A) one or more compounds containing isocyanategroups, B) one or more hydroxy-functional compounds which contain atleast one group selected from vinyl ethers, acrylates and methacrylateswhich react, with polymerization, with ethylenically unsaturatedcompounds on exposure to actinic radiation and C) optionally one or morecompounds containing NCO-reactive groups; and subsequently reacting theNCO-group-containing urethane, without further addition of compoundscontaining isocyanate groups, in the presence of an allophanatizationcatalyst, wherein the ratio of NCO groups of the compounds A) to the OHgroups of the one or more compounds B) and, where used, C) is from1.45:1.0 to 1.1:1.0.
 2. The radiation-curing allophanate according toclaim 1, wherein A) comprises hexamethylene diisocyanate, isophoronediisocyanate or 4,4′-diisocyanatodicyclohexylmethane.
 3. Theradiation-curing allophanate according to claim 1, wherein B) compriseshydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate orhydroxybutyl (meth)acrylate.
 4. The radiation-curing allophanateaccording to claim 1, wherein the ratio of NCO groups of the one or morecompounds A) to the OH groups of the one or more compounds B) andcompounds C) is 1.35:1.0 to 1.3:1.0.
 5. The radiation-curing allophanateaccording to claim 1, wherein the allophanatization catalyst is added ata rate of 200-600 ppm/h.
 6. The radiation-curing allophanate accordingto claim 1, wherein the reacting is carried out until the end producthas an NCO content of below 0.1% by weight.
 7. The radiation-curingallophanate according to claim 1, wherein no distillation is required toyield the radiation-curing allophanate having a residual monomer contentof less than 0.5% by weight and an NCO content of less than 1% byweight.
 8. The radiation-curing allophanate according to claim 1, withthe proviso that no distillation is performed.
 9. A coating compositioncomprising radiation-curing allophanate according to claim 1, b)optionally one or more polyisocyanates containing free or blockedisocyanate groups, which are free from groups that react, withpolymerization, with ethylenically unsaturated compounds on exposure toactinic radiation, c) optionally other compounds, different from a),which contain groups that react, with polymerization, with ethylenicallyunsaturated compounds on exposure to actinic radiation, and optionallycontain free or blocked NCO groups, d) optionally one or moreisocyanate-reactive compounds containing active hydrogen, e) initiators,optionally solvents, and g) optionally auxiliaries and additives.
 10. Asubstrate coated with the coating composition according to claim
 9. 11.The radiation-curing allophanate according to claim 1, wherein A)comprises hexamethylene diisocyanate.
 12. The radiation-curingallophanate according to claim 1, wherein A) comprises isophoronediisocyanate.
 13. The radiation-curing allophanate according to claim 1,wherein A) comprises 4,4′-diisocyanatodicyclohexylmethane.
 14. Theradiation-curing allophanate according to claim 1, wherein B) compriseshydroxyethyl (meth)acrylate.
 15. The radiation-curing allophanateaccording to claim 1, wherein B) comprises hydroxypropyl (meth)acrylate.16. The radiation-curing allophanate according to claim 1, wherein B)comprises hydroxybutyl (meth)acrylate.